This invention relates to a new stabilizer composition for enhancing the resistance to deterioration upon heating of vinyl chloride polymers, and to vinyl chloride polymers having enhanced resistance to deterioration in initial color, heat stability and clarity as a result of incorporating therein a stabilizer composition according to this invention.
There is a voluminous literature on the stabilization of vinyl chloride polymers. Patent disclosures of materials stated to be useful in minimizing deterioration of vinyl chloride polymers on heating number well over one thousand. Among the more important heat stabilizers in commercial use are mild alkalis such as sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, and the alkaline earth metals; inorganic and organic lead salts; organotin carboxylates, as disclosed by Quattlebaum in U.S. Pat. No. 2,307,157; organotin mercaptides as disclosed by Leistner in U.S. Pat. Nos. 2,641,588 and 2,641,598; various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol, pentaerythritol, organic phosphites, 1,2-epoxides, e.g., soybean oil epoxide, isooctyl epoxystearate, and the diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds, e.g., phenylurea, N,N'-diphenylthiourea, and 2-phenylindole. For detailed discussion of heat stabilizers for vinyl halide resins, reference may be made to the articles, L. I. Nass, in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed.) Vol. 12, pages 737 to 768 (1970); N. L. Perry "Barium-Cadmium Stabilization of Polyvinyl Chloride," Rubber Age 85 449-452 (June, 1959), and by H. Verity-Smith, British Plastics 27 176-179, 213-217, 307-311 (1954); the brochure by the same author The Development of the Organotin Stabilizer (Tin Research Institute, 1959) and the book La Stabilisation des Chlorures de Polyvinyle by F. Chevassus (Amphora, Paris, 1957).
The earliest disclosure of polyhydric alcohol containing stabilizers in vinyl chloride polymers is believed to be by R. Lally in U.S. Pat. No. 2,711,401 of July 21, 1955. Lally disclosed "a new composition of matter comprising in admixture of from 1 to about 5 parts of a organo-salt of a metal selected from the class of magnesium, calcium, strontium, barium, zinc, cadmium, mercury, tin and lead and from about 1 to about 5 parts of a compound selected from the class of aliphatic polyhydric alcohols having at least two and not more than nine hydroxyl groups and a boiling point not less than 250.degree. F., esters of aliphatic polyhydric alcohols said esters having at least two and not more than nine hydroxyl groups and a boiling point not less than 250.degree. F., and ethers of aliphatic polyhydric alcohols said ethers having at least two and not more than nine hydroxyl groups and a boiling point not less than 250.degree. F.", and rephrased this disclosure in simpler language as "the stabilizer of this invention is an admixture of a metallic soap and a aliphatic polyhydric compound." Lally lists the polyhydric compounds which he had found particularly useful as glycol, glycerol, sorbitol, pentaerythritol, glyceryl mono-stearate, glyceryl mono-oleate, glycol diethyl ether and glyceryl monophenyl ether, and in one example discloses as stabilizer an admixture of one part of glyceryl mono-stearate with one part of cadmium 2-ethylhexoate. Thus wherever Lally discloses a polyhydric alcohol ester it is an ester of an aliphatic acid.
Polyhydric alcohol containing stabilizers are also disclosed by S. Elliott in U.S. Pat. Nos. 2,861,052 of Nov. 18, 1958 and 2,918,451 of Dec. 22, 1959. Both Elliott's disclosures specify that the polyhydric alcohol is a primary aliphatic polyhydric alcohol having a boiling point at least 250.degree. F. and at least three hydroxyl groups of which at least two hydroxyl groups are free. Intimately admixed with the primary polyhydric alcohol Elliott in U.S. Pat. No. 2,861,052 disclosed a colorless Friedel-Crafts type catalyst, such as a halide of antimony, zinc, tin, titanium, zirconium, beryllium, boron, cadmium, and bismuth, and in U.S. Pat. No. 2,918,451, a colorless Friedel-Crafts type catalyst cation progenitor, such as an oxide, carbonate, hydroxide or carboxylic acid salt of the recited metals, together with an acid acceptor. In both disclosures Elliott states that the alcohols as defined can have ether or ester groups attached thereto, without disclosing or exemplifying any such ethers or esters. Elliott further points out that polyhydric alcohols with secondary or tertiary OH groups, even along with some primary OH groups, are undesirable. A. Hecker in U.S. Pat. No. 3,285,868 of Nov. 15, 1966 disclosed a stabilizer composition comprising a hydrocarbon substituted phenol and a polyvalent metal salt of a non-nitrogenous monocarboxylic acid along with a polyhydric alcohol of a certain structure to reduce or prevent a yellow tint introduced by the phenol in these compositions and further extend the stabilization obtained with a given amount of phenol and fatty acid salt. The polyhydric alcohols have the structure RCH.sub.2 C(CH.sub.2 OH).sub.3 where R is hydrogen or an alkyl or alkoxy group. The alkyl or alkoxy group may include hydroxyl or hydroxyalkyl groups. Polyhydric alcohols in Hecker's stabilizer composition include dipentaerythritol, tripentaerythritol, bis(trimethylolpropyl) ether, trimethylolpropane and trimethylolbutane, while pentaerythritol, glycerol, ethylene glycol, mannitol and sorbitol are deemed unsatisfactory. There is no disclosure of polyhydric alcohol esters by Hecker.
Another stabilizer composition comprising metal salts and polyhydric alcohols is disclosed by J. Scullin in U.S. Pat. No. 3,390,112 of June 25, 1968. Scullin's composition includes particularly polyhydric alcohols characterized as unsatisfactory by Elliott or Hecker or both, such as pentaerythritol, sorbitol, mannitol, methyl glucoside, and a polymeric polyhydric alcohol, together with a phenol and a barium and a cadmium salt, one of which has an aromatic anion and one an aliphatic anion. There is no disclosure of polyhydric alcohol esters in Scullin's patent. M. Gattenby in U.S. Pat. No. 3,479,308 of Nov. 18, 1969 disclosed plasticized vinyl chloride polymers comprising a combination of 2-6 carbon polyhydric alcohol partial fatty acid ester and polyethoxylated 2-6 carbon polyhydric alcohol partial fatty acid ester in relative proportions of 1 to 15 parts of the first ester to 0.5 to 10 parts of the second ester. The advantage of the selected polyhydric alcohol fatty acid esters is stated to be an improvement in antifogging properties of the plastic composition, that is the ability to cause moisture to condense on the plastic in the form of a transparent film instead of undesirable droplets or fog. Nothing is disclosed by Gattenby of a relationship between antifogging properties and heat stability of the vinyl chloride polymer composition, and in fact certain polyhydric alcohol fatty acid esters used by Gattenby have a deleterious effect on heat stability.
A. Hecker in U.S. Pat. No. 3,558,537 of Jan. 26, 1971 disclosed a stabilizer composition capable of increasing the resistance of polyvinyl chloride both to heat deterioration and to fogging comprising a zinc salt of a monocarboxylic acid and a partial ester of a polyglycerol with an unsaturated aliphatic monocarboxylic acid, not more than 75% of the hydroxyl groups of the polyglycerol being esterified.
Tenneco Chemicals' British Pat. No. 1,077,108 of July 26, 1967 discloses a stabilized vinyl halide resin containing an inorganic filler and a stabilizer comprising an organic nitrogen compound having three nitrogen atoms linked to one carbon atom and an anhydride of a polycarboxylic acid. As an additional non-essential ingredient, a polyhydric alcohol having 4 or more hydroxyl groups can be included. There is no disclosure of polyhydric alcohol esters in this patent.
Tenneco Chemicals' British Pat. No. 1,163,750 of Sept. 10, 1969 discloses a stabilized vinyl halide resin containing a metal silicate filler and a polyhydric alcohol, such as ethylene glycol, neopentyl glycol, trimethylolpropane, 1,2,6-hexanetriol, methyl glucoside, pentaerythritol, sorbitol or mannitol. There is no disclosure of polyhydric alcohol esters in this patent.
Kureha Kagaku's British Pat. No. 1,140,652 of Jan. 22, 1969 discloses improved vinyl chloride polymer compositions stabilized with a zinc, calcium, or magnesium fatty acid salt, a polyhydric alcohol, such as sorbitol, mannitol, and pentaerythritol, and to improve the compatibility and clarity of the composition a fatty acid ester of sucrose.
When this art is considered as a whole, it is evident that the record of polyhydric alcohol utilization in vinyl chloride polymer stabilizers encompasses both successes and unsolved problems. There remains a need for an economical ingredient of a stabilizer composition that would maintain the favorable properties of polyhydric alcohols and overcome the drawbacks repeatedly noted in the art.